Generally, this invention relates to an apparatus for detection of a controlled substance via Surface Plasmon Resonance Spectroscopy (SPRS). Specifically, this invention relates to a new biosensor element to be used in combination with SPRS for immunochemical detection of an explosive substance for security and anti-terrorism purposes. This invention also relates to methods for using this biosensor element in combination with SPRS for the aforementioned purposes in different conditions such as a gas phase, a liquid phase or a solid phase (e.g., gel state).
Biosensors are becoming a reliable and economical method of analysis for compounds from the areas of environmental chemistry to medicine. These methods are selective due to the very specific nature of the antibody-antigen reaction and generally offer low limits of detectability. In most applications, though, these immuno-biosensors have been used primarily for solution based analyses. One example is a biosensor for the detection of TNT and RDX developed by the U.S. Naval Research Laboratory which purportedly can reliably detect these compounds in the concentration range of 20-1200 ppb (Ngeh-Ngwainbi et al., 1986, J. Am. Chem. Soc., 108,18: 5444-5447). This instrumental method purportedly utilized an aqueous competitive fluorescent tagged antigen competition scheme with fluorescence detection. Since these techniques are for the detection of explosives only in solution, their subsequent applications where detection of explosives in air is necessary are quite limited.
Although this work has been disputed, Gas Phase Immunoassay (GPI) was purportedly demonstrated by Guilbault in the vapor phase detection of cocaine and the insecticide parathion. In the Guibault effort, parathion was purportedly detected at 35 ppb in air, its saturated concentration, and the immunochemical reaction was purportedly found to be reversible and reproducible to within 6%. Response time was purportedly less than a minute with no preconcentration step. The antibody was also purportedly found to react with other related pesticides. However, since the reaction with pesticides only occurred at high pesticide concentrations, the assay was considered to be quite specific, or having minimal non-specific interactions at other than high concentrations. It was, however, subject to the limitations of the immunoassay method.
For such experiments, the antibodies for the respective compounds were immobilized onto a piezoelectric crystal by simply drying the protein onto the surface. This limited the number of antibody proteins available to undergo the antibody-antigen reaction since some receptors were buried under others (Ngeh-Ngwainbi et al., 1986, J. Am. Chem. Soc., 108,18: 5444-5447; Hahn and Guibault, 1988, Ph.D. thesis).
Due to the limitations of utilizing a gas phase immunoassay reaction, an improved method for detecting the reaction is needed. Unfortunately, few analytical methods have appeared to be applicable to the detection of the immunochemical reaction in the gas phase. In Guibault""s method for the detection of cocaine and parathion, as in several others (Suleiman and Guibault, 1994, Analyst 119: 2279-2282; Suleiman and Guibault, 1991, Analytical Letter 24: 1283-1292; Attili and Suleiman, 1996, Microchemical Journal, 54: 174-179), the immunochemical receptor, the commercial antibody for parathion, for instance, was immobilized onto a piezoelectric crystal. The immunochemical chemical reaction was observed as a function of the change in the shear mode of the quartz crystal which changes due to mass loading of the analyte. This sensitive analytical method is termed the Quartz Micro Balance (QMB). The Bofors Applied Technologies method uses this detection method for their TNT biosensor (Rouhi, 1997, CandEN, March 10, 14-22).
This invention is based on a wholly different detection method using spectroscopy. This is Surface Plasmon Resonance Spectroscopy (SPRS) which is described in detail below.
SPRS has previously been used for a liquid phase, such as to detect the antibody-hapten reaction in liquids from the tip of an optical fiber probe. Katerknap, et al. (Acta., 1995, 119: 63-72) described the use of this form of spectroscopy which can purportedly detect the immunochemical interaction for bovine serum albumin (BSA)/anti-BSA at 0.2 ug/mL in solution. Ehler, et al. (Ehler and Noe, Langmuir, 1995, 11:4177; Ehler, Malmberg, Noe, 1997, J. Phys. Chem., 101:1268-1272) utilized a more traditional geometry for SPRS consisting of a glass slide with a sputtered metal surface interfaced onto a movable prism. By arranging a self assembled monolayer (SAM) on the surface of the slide, they were able to detect differences in the thickness and the calculated tilt angle of a self assembled monolayer on the metal surface with SPRS in the gas phase. For example, difference in the carbon chain length of two methyl units was easily detectable. Unfortunately, there has been a long felt, but unsatisfied need for a system that achieves the high specificity and low detection levels desired for security and other applications.
When a device such as an explosive detection system is designed for use, it needs to satisfy the common requirements for, first of all, specificity; second, simplicity; third, convenience; and fourth, speed. Some problems existing in this specific field are the complexity of the existing methods and equipments, and the inability of detection of an explosive or other controlled substance in a gas phase using a simple device. Substantial attempts by those skilled in the art to fill the need for a detection device that is simple, yet specific have not been successful, possibly because of failure to understand the nature of problems. In fact, previous art seems to teach away from the technical direction in which the patentee went. It is this invention that satisfies the need. A simple but effective biosensor element innovatorily advances the detection process and equipment needed when it is combined with a SPRS technology. From this perspective, this invention seems to represent not a just gradual slope of improvement but rather an innovative creation of a detection device and a new direction for such devices.
In view of the foregoing, it is a primary object of the present invention to provide an innovative biosensor element to be used in combination with SPRS for immunochemical detection of an explosive substance, such as for security and anti-terrorism purposes. The biosensor comprises a specially designed surface which can be optically coupled to a Surface Plasmon Resonance (SPR) spectrometer. The biosensor surface can be comprised of a substrate of the same material as the SPR optical component and can be metallized. A chemical layer consisting of a thiol can be reacted onto the surface as a Self Assembled Monolayer (SAM). Onto this reactive SAM, biomolecules such as antibodies, antibody fragments, proteins or other substances can be reacted with the SAM producing a biosensor surface which can be utilized in the detection process.
Thus, it is an object of this invention to provide a biosensor element for detection of a controlled substance via Surface Plasmon Resonance Spectroscopy (SPRS). The controlled substances may include, but not limited to, a highly explosive component, a drug or even an accelerant such as of interest in an arson investigation or the like.
It is also an object of this invention to provide a biosensor element for detection of a harmful biological agent in air via SPRS, such as anthrax spores, bacteria, fungal spores and viruses, for anti-biological weapon or air quality control and environmental pollution watch or the like.
It is still another object of this invention to provide a biosensor element for detection of a controlled substance in a liquid phase via SPRS such as a drug in a blood sample.
This invention also relates to methods for using this biosensor element in combination with SPRS for the aforementioned purposes in different conditions such as a gas phase, a liquid phase or a solid phase (e.g., including a gel state).
Naturally, further objects of the invention are disclosed throughout other areas of the specification, drawings, and claims.